In an effort to prevent electrical shock, circuit interrupting devices are designed to interrupt power to various loads, such as household appliances and consumer electrical products. In particular, electrical building codes in many states require that electrical circuits in residential or commercial bathrooms and kitchens be equipped with circuit interrupting devices. Household appliances are typically connected to electrical receptacles having at least a hot terminal and neutral terminal; the terminals are usually implemented as receptacles to which an electrical plug of the household appliance is attached. When an appliance is working properly, the current used by the appliance flows from the hot terminal of the electrical receptacle through the appliance and back to the neutral terminal of the receptacle. When, however, a person uses an appliance in the rain or near a wet surface, an extra path may be created from the appliance through the person and the water to ground. Consequently the amplitude of the current flowing from the receptacle to the household appliance is not be equal to the amplitude of the current flowing from the appliance back to the neutral terminal of the receptacle; that is, part of the current has been diverted through the extra path. Therefore, an imbalance in the current flow is created; this imbalance is typically referred to as a ground fault.
There exists a circuit between the receptacle and a power source which provides power to the receptacle. In particular, a hot or phase wire from the power source is connected to a phase terminal of the receptacle and a neutral wire from the power source is connected to a neutral terminal of the receptacle. A circuit interrupting device, such as a ground fault circuit interrupter (GFCI) is placed in the receptacle and is connected to the phase and neutral terminals of the receptacle. Thus, when a household device is plugged into the receptacle the hot or phase wire extends from the power source to the receptacle through the GFCI to the household appliance. Also, a neutral connection extends from the household appliance to the receptacle through the GFCI and onto the power source's neutral terminal. As such, the GFCI is positioned as part of a circuit comprising the power source, the conductors connecting the power source to the receptacle, conductors connecting the receptacle to the appliance and conductors from the appliance to the receptacle and back to the power source. There is a switching device within the GFCI that—when closed—allows the current in the circuit to flow from the power source through the GFCI to the appliance and from the appliance back to the receptacle through the GFCI and back to the power source. Circuit interrupting devices are designed to detect current imbalances and activate their switching device so as to disconnect power from the receptacle thus disconnecting power from a household device plugged to the receptacle when a ground fault is detected.
Presently available circuit interrupting devices, such as the device described in commonly owned U.S. Pat. No. 4,595,894, use a trip device to mechanically break an electrical connection between one or more input and output conductors of the circuit interrupting device. Such devices are resettable after the detection of a ground fault, for example. In particular, a trip device is used to cause the mechanical breaking of the circuit. The trip device includes a solenoid (or trip coil). As a feature to test the trip device and circuitry used to sense faults, a test button is used to initiate a manual test of the GFCI. In addition, a reset button is used to reset the electrical connection between input and output conductors of the GFCI.
Electrical receptacles within which are located circuit interrupting devices (such as GFCIs) have a line side, which is connectable to an electrical power supply, and a load side, which is connectable to one or more loads (e.g., other receptacles). Where a circuit interrupting device includes a user accessible connection, the load side connection and user accessible connection are typically electrically connected to each other. An example of the user accessible connection is a two hole or three hole receptacle used for AC outlets; the connection is implemented as receptacle terminal in which a plug can be connected providing power to an electrical household device, for example. Wires from the power source are connected to the line side of the GFCI receptacle and wires from one or more loads (e.g., other receptacles) are connected to the load side of the GFCI receptacle. Instances, however, may occur where the circuit interrupting device is improperly connected to the external wires so that the load wires are connected to the line side connection and the line wires are connected to the load side connection; this is known as reverse wiring. In the event the circuit interrupting device is reverse wired, fault protection to the user accessible load connection may be eliminated, even if fault protection to the load side connection remains. Thus, there is a need for electrical receptacles that are capable of detecting when reverse wiring has occurred.
Moreover, in an effort to limit the exposure of children to electrical shock, the National Electrical Code (NEC) requires that in buildings where the predominant function of such buildings is to provide shelter for children (e.g., schools, nurseries, daycare facilities, hospitals, residential housing), tamper-resistant electrical receptacles and ground fault circuit interrupters (GFCI) should be designed within an electrical distribution system throughout such residential or commercial buildings. In particular, since a large percentage of electrical receptacles used in residential buildings are installed near the floor, a person, such as a young child or infant, for example, can insert small elongated articles into the cover apertures of the electrical receptacle. More particularly, if the child inserts an object made of conductive material including but not limited to a metal article, electrical shock may result. Another possibility is where an infant or a young child places his or her mouth over an electrical receptacle. Accordingly, a burn or shock may result when the child's wet mouth makes contact with one of the terminals; this is because a path is caused to exist from the hot receptacle terminal through the child to ground creating a ground fault. Ground fault circuit interrupters, however, only disconnect the power supplied to the circuit after a child has made contact with a conductor. Thus, without a tamper resistant electrical receptacle, a child may still experience an electrical shock.
Commonly owned, co-pending patent application Ser. No. 10/690,776, filed Oct. 22, 2003 which is incorporated herein in its entirety by reference, describes a family of resettable circuit interrupting devices (e.g., GFCI receptacles) capable of preventing electric power from being accessible to users of such devices when these devices are reverse wired. Each device has a reset lockout system that prevents the device from being reset when the device is not operating properly. When the device is not reset and if such device is reverse wired, no power is available to any user accessible receptacles and/or plugs located on the face of the devices. The device is preferably shipped in a trip condition, where no electrical connection exists between line and load terminals and no electrical connection exists between load and face terminals. Thus, in the trip condition the three terminals are electrically isolated from each other. If the device is wired in reverse, the device cannot be reset.
However, presently there are no devices within the family of resettable circuit interrupting devices having reverse wiring protection (e.g., such as a shutter lock) that includes a tamper-proof feature. Therefore, there is a need for a simple, effective, efficient, low-cost electrical receptacle that is tamper-proof and provides protection from reverse wiring.